Investigation of the direct band gaps in Ge1−xSnx alloys with strain control by photoreflectance spectroscopy

Abstract

Unstrained and compressive-strained Ge1−xSnx alloys were grown on InGaAs buffer layers by molecular beam epitaxy. Photoreflectance at room temperature determines the direct bandgap energies of Ge1−xSnx alloys from the maxima of the light- and heavy-hole bands to the bottom of Γ valley. The lowest transition energies from photoreflectance are consistent with the energies derived from photoluminescence. The calculated bowing parameter is 2.42 ± 0.04 eV for the direct band gap of Ge1−xSnx alloys. The dilational and shear deformation potentials of the direct band gap are −11.04 ± 1.41 eV and −4.07 ± 0.91 eV, respectively. These basic material parameters are important in designing optoelectronic devices based on Ge1−xSnx alloys.